The present invention relates to a method for measuring a halftone dot area rate or a halftone picture density.
In a conventional halftone dot area rate measuring means, since the gradation of a measured halftone picture image varies, the aperture diameter which will determine the measured area is preferably small. However, if it is too small, when the halftone picture image is measured, the value which is measured will vary depending on the relative position of the aperture and the halftone dot.
Large variances do not arise when the number of scanning lines per distance increment is large. Large variances often occur when the number of scanning lines is small, e.g., a gauge having about ten lines per centimeter for printed matter. Such a gauge is printed in a relatively small area such as 5 mm.times.6 mm, and hence this problem can be resolved only by expanding the diameter of the aperture or the measuring area.